The present invention relates to drilling apparatus for use in underground exploration of petroleum products. These drilling apparatus usually comprise a rotary drilling bit with a plurality of cutters rotatably supported in a rolling bearing on a trunnion of the drilling bit body. These assemblies usually also include an edge ring provided with a seal which is fixed in the bored hole of the rotary cutter between the rollers of the roller bearing and the drilling bit body. These rings with seals serve to guide the rollers axially to one side.
Rotary drilling bits of this general type are known in the prior art. For example, a German application No. 2,021,011 shows a drilling bit wherein a slip ring with a sealing ring is provided between the edge ring fixed in the rotary cutter and the trunnion of the drilling bit body which laterally faces a slip ring with a sealing ring installed towards the side of the drilling bit body attached in a holder bolted to the trunnion. This arrangement has several disadvantages and drawbacks. For example, it has been observed that a comparatively large amount of axial space is needed to house the sealing elements requiring that the trunnion must be constructed in cantilever fashion at a relatively large distance from the drilling bit body and consequently the rolling bearing occupies a large space in the drilling bit body. Therefore, the loading forces of the rotary cutters cause an unfavorably high bending moment at the trunnion. Additionally, the endurance and load capacity of the rotary cutter have been found to be inadequate since the relatively long trunnion of the drilling bit body has a tendency to be distorted and bend in operation as the result of high impact loads whereby the bearings of the rotary cutters operate in a skewed or tilted position and thereby fail prematurely. Consequently the useful life of the known rotary drill bits is quite abbreviated.